Many kinds of board products have been made from woody plant fibers in the form of chips, slabs, strands, shreds, particles, sawdust, shavings, comminutions, and other fiber forms. Such fibrous materials have been bound together using a variety of binders and forming methods to produce boards or panels referred to as chipboard, particle board, fiberboard, strand board, wood-wool board, veneer board, and pressboard, to name just some.
It is known that the woody rinds of grasses such as sugarcane and sweet sorghum can be used in producing some of such boards.
United States patents have been granted on various improvements relating to panels and boards, and/or their manufacture, including the following:
2,592,470 (Ryberg) PA1 2,648,262 (Croston et al.) PA1 2,717,420 (Roy) PA1 2,853,413 (Christian) PA1 3,164,511 (Elmendorf) PA1 3,464,881 (Miller et al.) PA1 3,464,877 (Miller et al.) PA1 3,567,511 (Tilby) PA1 3,690,358 (Tilby) PA1 4,025,278 (Tilby) PA1 4,212,616 (Tilby) PA1 4,312,677 (Tilby et al.).
While some of these patents relate to the solid boards, many relate to lighter and less expensive boards and panels. A long-standing problem or shortcoming of the latter boards and panels is their structural weakness. Because of this, few of them have excellent weight-bearing and structural characteristics; such boards and panels often serve lesser covering, underlying, or decorative needs. Many of such boards and panels have little ability to serve in situations exposing them to weather, because weakening can occur.
In many cases, the strength of such panels and boards is provided primarily by the binder rather than by the fibers used in manufacture In some cases, a degree of strength is achieved by the degree of packing. In others, the use of large amounts of binder per unit volume of product increases the cost of such panels.
Such panels not only are lacking in structural strength, but typically do not have good insulating qualities. Because of this the usefulness of such panels is often quite limited.
Manufacture of such panels and boards has been carried out in various methods, some requiring complex extrusion equipment or other manufacturing equipment. The processes used in making such panels and boards often require extended periods to achieve drying throughout the cross-section of the board or panel, and significant amounts of energy.
A major problem in many developing countries and elsewhere is the shortage of high-quality building materials or, stated differently, the high cost of materials used for various building needs, including residential housing. In many cases, locally manufactured materials may not be available, requiring importation which adds to costs.
There is a clear need for an improved apparatus and method for manufacture of structural panels. Such apparatus must be low in cost and able to produce low-cost, light-weight structural panels with good load-bearing qualities, good insulative qualities, and good weather-resistance. An apparatus for production of such structural panels from sugarcane and sorghum rinds, particularly in developing countries, would provide important advantages.
A structural panel has been developed which meets the above-noted requirements and fills the above-noted needs. Such structural panel is made from the rinds of grasses selected from the group consisting of sugarcane and sweet sorghum, i.e., those grasses having woody rinds surrounding a pithy center, and has significantly improved structural characteristics. The apparatus and method of this invention are highly useful in high-speed manufacture of such panel.
Such structural panel is formed of a pile of rind fiber-bundle strands randomly oriented in substantially parallel planes. The strands are substantially straight and of sufficient length such that most have a stalk node thereon. Each strand has a multiplicity of contact points therealong with other strands of the pile, and a binder which coats the strands interconnects them at such contact points to form a substantially rigid structure. The coated interconnected strands define voids within the pile.
In such structural panel, strand length and substantial straightness are matters of considerable importance. The strands are made of rind fiber bundles, a term used to describe narrow strips of dried woody sugarcane or sorghum rind which, e.g., are split away from half-billet rinds in sugarcane or sweet sorghum processing using the so-called Tilby separation system. Very short, very thin, and/or very curly strands are not usable in such structural panel because they would not impart the desired structural strength.
That is, each strand is preferably at least 15 cm long, while a length of 20-30 cm is very highly preferred as offering the best panel qualities. Such fiber-bundle strands, which have a thickness equal to the thickness of the sugarcane or sorghum rind, are preferably at least about 0.10 cm wide, while widths of about 0.15-0.40 cm are very highly preferred. Dimensions of this general order will assure that the fiber-bundle strands are substantially straight as required.
Such structural panel is very light in weight, preferably having a density as low as about 0.15-0.25 g/cc. Yet such panel has superior structural qualities. In such structural panel the voids mentioned above are sufficient to allow air flow through the pile. This is so even though the panel is quite thick when compared to many other panels and boards.
The light weight and openness of such panel, and the fact that despite such qualities the panel has excellent structural strength, are related to the aforementioned random arrangement of the fiber-bundle strands in substantially parallel planes. Achieving an acceptable random arrangement in substantially parallel planes, and doing so in a high-speed manufacturing operation, are not easily accomplished.
The problems encountered include insufficient randomness, bunching, a need for strand redistribution after initial laying of a strand pile, and many others. Such problems may result in panel weakness, unacceptable variations in panel strength, and unsightly appearance. Even manual readjustment of an improperly laid pile can lead to such problems.
It is desirable for the aforementioned structural panel to have substantial width, given its intended uses in building construction or the like. Substantial panel width, and the resulting need for substantial width in a pile of fiber-bundle strands during manufacture of the paneling, tend to exacerbate the problems of achieving acceptable randomness in a random arrangement of fibers in generally parallel planes.
There is a need for a method and apparatus for creating, from a collection of strands, a considerable volume of strands arranged with suitable randomness in substantially parallel planes. A method and apparatus for piling such strands with acceptable randomness in a continuous high-speed operation would allow commercial manufacture of high-quality structural panel from the rinds of sugarcane, sweet sorghum and the like.